Electrical wire having resin composition covering

ABSTRACT

An electrical wire and a method of making the electrical wire are provided. The electrical wire includes a conductor and an electrically insulating covering formed on the conductor. The electrically insulating covering is a resin composition including a first polymer, a second polymer and filler particles. The first polymer has a higher bonding affinity to the filler particles than the second polymer. The filler particles are coated with the first polymer and the coated filler particles are embedded in a matrix of the second polymer. The electrical wire is suitable for use in motor vehicles.

BACKGROUND OF THE INVENTION

[0001] 1. Field of Invention

[0002] This invention relates to an electrical wire having a halogen-free resin composition as an electrically insulating covering on an electrical conductor core.

[0003] 2. Description of Related Art

[0004] Polyvinyl chloride has been much used as the covering material of electrical wire used in automobiles, because it is superior in properties such as mechanical strength, extrusion processability, flexibility and coloring property. However, with recent concern for the global environment, halogen-free resin material has come to be used for the production of automobile parts including the covering of electrical wires in an automobile in place of polyvinyl chloride, because polyvinyl chloride discharges a harmful halogen gas on combustion.

[0005] A halogen-free resin composition, in which a metal hydroxide is blended with a polyolefin-based polymer as a flame-retardant, is known as a wear resistant resin composition that does not generate poisonous gas such as a halogen gas on combustion. See, for example, JP-A-7-176219 and JP-A-7-78518. So that the flame-retardant resin composition has a self-extinction property, a large quantity of filler must be added. However, the large quantity of filler causes problems with various aspects of mechanical strength, including reductions in wear resistance, tensile strength and the like.

[0006] Various fillers have been proposed for improving the properties of such resin compositions. For example, metal oxides such as titanium oxide and the like are used as a pigments. Metal hydroxides such as magnesium hydroxide, aluminum hydroxide and the like, as mentioned above, are added in order to impart flame resistance to resin compositions. Calcium carbonate, talc, clay, silica and the like are used to increase bulk. Carbon fiber, glass fiber, talc, mica and the like are added for reinforcement.

[0007] However, polymer resins typically do not have a great affinity for such fillers. Accordingly, the filler particles often become mutually coagulated to form lumps of filler particles in a resin phase when the filler is compounded with the resin. Thus, it is difficult to achieve a resin having a homogeneous distribution of the filler in the resin phase.

SUMMARY OF THE INVENTION

[0008] To prevent coagulation of the filler in the resin composition, surface treated fillers are often employed. Surface-treatment agents include silane-based agents, titanate-based agents, aluminum-based agents, fatty acid-based oils and fats, waxes, surfactants, and the like. However, use of such surface-treated fillers can reduce mechanical strength, cause whitening of the wire covering on bending, result in poor processing properties, and the like.

[0009] Accordingly, an object of this invention is to provide an electrical wire having a resin composition covering in which a filler is homogeneously dispersed without coagulation. Another object of this invention is to provide a method for producing such a wire.

[0010] According to this invention, there is provided an electrical wire having a conductor and an electrically insulating covering on the conductor. The covering is a resin composition comprising at least one first polymer, at least one second polymer and filler particles. The at least one first polymer has a higher bonding affinity for the filler particles than the at least one second polymer. The filler particles are coated with the first polymer and the coated filler particles are embedded in a matrix of the second polymer.

[0011] According to this invention there is also provided a method of making an electrical wire which comprises forming a resin composition comprising at least one first polymer, at least one second polymer and filler particles. The first polymer has a higher bonding affinity for the filler particles than the second polymer. The filler particles are coated with the first polymer and the coated filler particles are embedded in a matrix of the second polymer. The method also comprises applying the resin composition to an electrical conductor to form an electrically insulating covering thereon. Forming the resin composition can comprise first kneading the filler particles and the first polymer to form a mixture and subsequently kneading the mixture and the second polymer, or alternatively kneading the filler particles and the first and second polymers together at the same time.

[0012] These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Various exemplary embodiments of this invention will be described in detail, with reference to the following figures, wherein:

[0014]FIG. 1 is a micrograph produced by an electron microscope showing the structure of the resin composition obtained in Example 1.

[0015]FIG. 2 is a micrograph produced by an electron microscope showing the structure of the resin composition obtained in Comparative Example 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0016] In the present specification, including the claims, the term “filler” refers not only to mere fillers, but also to various additives and/or compounding agents that are conventionally added to improve resins.

[0017] The filler used in this invention may either be an inorganic filler or an organic filler. Inorganic fillers are preferred. Examples of suitable fillers include carbon materials, metal oxides, metal hydroxides, metal carbonates, metal sulfates, metal silicates, metal nitrides and combinations thereof. Metal compounds can include metals such as alkali metals, alkaline earth metals and transition metals. These fillers can be used alone or in combination. Of the metal compounds, metal hydroxides, such as magnesium hydroxide, aluminum hydroxide and the like, are preferred as fillers in resin compositions for electric wire because the compositions impart flame retarding properties. The resin compositions of this invention are, thus, desirably fire resistant compositions. For this purpose, the resin composition is preferably free of fibrous fillers. Preferably a metal hydroxide, or mixture of metal hydroxides, is the only filler present in the resin composition.

[0018] The filler particles used in this invention may be untreated or treated. Preferably the filler particles of this invention have been subjected to surface treatment with a coupling agent prior to mixing with the first and second polymers. Coupling agents can include silane coupling agents, fatty acids or salts of fatty acids. Since the dispersibility of the filler is improved by the first polymer coating, the filler coated with first polymer according to this invention can have high dispersibility without surface-treatment with the coupling agent. Silane coupling agents include, for example, aminosilane coupling agents, vinylsilane coupling agents, epoxysilane coupling agents, methacryloxysilane coupling agents, and the like. Exemplary fatty acids or salts thereof include higher fatty acids (e.g. having at least 12 carbon atoms), such as stearic acid, oleic acid, or the like, and their salts.

[0019] The first polymer has a bonding affinity for the filler. The first polymer, which is used to coat the particle surface of the filler, is preferably a polymer having a reactive functional group that promotes binding of the first polymer with the filler particle surface. Exemplary functional groups include carboxylic acid groups (including carboxylic acid ester groups), carboxylic anhydride groups, epoxy groups, hydroxy groups, amino groups, and the like.

[0020] These functional groups can be introduced to the first polymer by conducting polymerization using a monomer having such a functional group, or by graft-copolymerizing a monomer having the functional group to a skeleton polymer. In various exemplary embodiments, functional groups are present on the first polymer before the first polymer is mixed with the filler particles. Polymers having carboxylic acid groups or carboxylic acid anhydride groups, have a high affinity for inorganic fillers, and in particular for metal hydroxides. To introduce carboxylic acid groups or carboxylic anhydride groups, a monomer having an unsaturated carboxylic acid group or its anhydride or ester can be employed. Exemplary compositions include maleic acid and fumaric acid, and anhydrides, monoesters or diesters thereof, and the like.

[0021] Epoxy groups can be introduced to the first polymer by employing compounds having glycidyl groups, such as, for example, methyl glycidyl ether, butyl glycidyl ether, phenyl glycidyl ether, and the like.

[0022] The ratio of the monomer having the functional group to the total polymer is typically from about 0.01% to about 30% by weight and preferably from about 0.1% to about 10% by weight.

[0023] Exemplary first polymers, to which the functional group is introduced, include, but are not limited to, propylene homopolymers, propylene block or random copolymers, high density polyethylenes (HDPEs), linear low density polyethylenes (LLDPEs), low density polyethylenes (LDPEs), ultra low density polyethylenes, polybutenes, polystyrenes, ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, ethylene-methyl acrylate copolymers, ethylene-propylene rubbers, ethylene-butene rubbers, olefin-based elastomers (e.g., poly(propylene-ethylene/propylene) copolymers and the like), and styrene-based elastomers. Styrene-based elastomers can include, for example, block copolymers having polystyrene segments and rubber segments, such as polybutadienes (e.g., SBS, SBR), polyisoprenes (e.g., SIS,SER), ethylene/butadienes, the hydrogenated products of such compounds (SEBS, HSBR, SEPS, HSIR).

[0024] Polymers comprising one or more acid anhydride group have a high affinity for inorganic fillers, and in particular, metal hydroxides. Exemplary polymers containing an acid anhydride group that have a good affinity for fillers include, but are not limited to, acid anhydride-modified ethylene-vinyl acetate copolymers, acid anhydride-modified ethylene-ethyl acrylate copolymers, acid anhydride-modified ethylene-propylene rubbers, acid anhydride-modified low density polyethylenes, acid anhydride-modified linear low density polyethylenes, acid anhydride-modified poly(propylene-ethylene/propylene) copolymers, acid anhydride-modified styrene-butadiene rubbers, and acid anhydride-modified hydrogenated styrene-butadiene rubbers.

[0025] In various exemplary embodiments of this invention in which a polymer modified with a carboxylic acid group or a carboxylic acid anhydride group is used as the first polymer, and a metal hydroxide is used as the filler, the composition preferably includes no component, other than the metal hydroxide, which reacts with the carboxylic acid or acid anhydride group. It is desired that the first polymer bonds directly to the metal hydroxide particles, during mixing or extrusion, to improve the mixing and dispersion of the metal hydroxide particles in the composition.

[0026] The amount of the first polymer used for coating the filler may be suitably selected according to the filler that is employed, and is not particularly limited. However, the first polymer is preferably present in an amount that does not exceed about 50% by weight, relative to the total polymer content. The first polymer is more preferably present in an amount between about 3% and about 40% by weight. The second polymer is, thus, preferably present in an amount of at least about 50%, more preferably in an amount of from about 60% to about 97%, by weight.

[0027] The resin composition used in this invention includes the filler coated with the above-mentioned first polymer and the second polymer, which is different from the first polymer. All of the polymers used in the resin composition are preferably halogen-free. In various exemplary embodiments, there are no polymer components present other than the first and second polymers. For example, in such embodiments where the resin composition includes only a single first polymer and only a single second polymer, there are only two polymer components in the resin composition.

[0028] The second polymer is not particularly limited, and may be selected with respect to its compatibility with the first polymer, and the use of the resulting resin composition. For coating an electric wire, an olefin-based polymer is preferred as the second polymer. Exemplary olefin-based polymers include propylene polymers such as homopolymers or propylene random or block copolymers (e.g. with ethylene); polyethylenes such as high density polyethylenes, linear low density polyethylenes, low density polyethylenes, ultra low density polyethylenes, and the like; polybutene polymers; polystyrenes and styrene copolymers; ethylene copolymers such as ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, and the like; olefin-based elastomers such as poly(propylene-ethylene/propylene) copolymers and the like; and styrene-based elastomers such as styrene-butadiene block copolymers, styrene-ethylene-propylene block copolymers, or copolymers that are obtained by saturating unsaturated double bonds in these copolymers by hydrogenation, and the like. These polymers can be used alone or in combination. For processing reasons, a single second polymer is preferred.

[0029] When the first polymer is an acid anhydride-modified polymer, it is preferred that the second polymer is a propylene polymer, an ethylene polymer or a propylene/ethylene copolymer.

[0030] Exemplary propylene polymers include propylene homopolymers and propylene copolymers having propylene as a main component (e.g., 50% by weight or more). Such propylene polymers can include propylene-ethylene block or random copolymers and the like.

[0031] Exemplary ethylene polymers include ethylene homopolymers and ethylene copolymers having ethylene as a main component (e.g., 50% by weight or more). Such ethylene polymers can include ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, ethylene-methyl methacrylate copolymers, and the like.

[0032] The resin composition used as a wire covering according to this invention can be produced by first mixing the filler and the first polymer. Alternatively, since the first polymer has a higher affinity for the filler than the second polymer, the first polymer preferentially coats the filler particles. Accordingly, the composition can be made by simultaneously mixing and kneading the filler, the first polymer and the second polymer.

[0033] In this regard, the production process for the resin composition according to this invention is not particularly limited. The resin composition may be produced by kneading the filler and the first polymer, and subsequently kneading the obtained mixture and the second polymer. Alternatively, the resin composition may be produced by simultaneously kneading the filler, the first polymer and the second polymer. Since the first polymer has higher affinity for the filler than the second polymer, it more easily adheres to the filler particles than the second polymer. Therefore, a morphology can be achieved in which the first polymer coats the filler particles and the second polymer fills the space between the coated filler particles. Such a morphology is known as a “spotted” or “island” structure, in which the second polymer is in “continuous phase” or a matrix, and the coated filler particles are in “discontinuous phase.” This morphology is later described and illustrated with reference to a electron micrograph of the resin composition in the Examples.

[0034] The proportion of the filler in the resin composition may be suitably selected according to the use of the resin composition, the types of first polymer and second polymer that are selected, the type of the filler, and the like. Alternatively, the proportion of the filler in the resin may be a conventional proportion. However, the coated filler in this invention has good dispersibility and is therefore homogeneously dispersed in the polymer, so that in suitable cases a larger quantity than a conventional compounding amount can be included. Alternatively, a smaller amount of filler may used to obtain the same effect.

[0035] In addition to the filler, various compounding agents can be added to the resin composition according to this invention. Exemplary compounding agents include those conventionally used in electric wire-coating resin materials. For example, the compounding agents can include thermal stabilizers such as oxidation inhibitors and the like; metal deactivators such as copper inhibitors and the like; lubricants such as fatty acid-based lubricants, fatty acid amide-based lubricants, metal soaps, hydrocarbon-based lubricants (waxes), ester-based lubricants, silicone-based lubricants and the like; coupling agents; softening agents such as process oils and the like; crosslinking agents; and the like.

[0036] The resin composition of this invention can be crosslinked if desired. For, for example, such cross linking may be desirable in applications if high heat resistance is required. Cross-linking can be carried out using a chemical cross-linking agents or using radiation (for example, ultra violet rays radiation, electron beam radiation, and the like). In various exemplary embodiments, the polymers of the resin composition are not cross-linked. In such embodiments, the composition is free from cross-linking agents, such as peroxide. Further, in various exemplary embodiments, the composition as applied as a wire covering, is free from cross-linking agents and decomposition products of cross-linking agents.

[0037] The resin composition of this invention can be crosslinked, when high heat resistance is desirable. The crosslinking can be carried out by compounding a chemical crosslinking agent, but may also be carried out by radiation. For example, ultraviolet radiation, electron beam radiation, and the like, can be employed.

[0038] A particularly preferred resin composition for the electric wire covering is one that contains from about 60 to about 97 parts by weight (preferably from about 70 to about 90 parts by weight) of a polypropylene polymer, from about 3 to about 40 parts by weight (preferably from about 10 to about 30 parts by weight) of a polymer modified with from about 0.1 to about 10% by weight of a monomer that contains an acid anhydride group, and from about 30 to about 200 parts by weight (preferably from about 50 to about 160 parts by weight) of a metal hydroxide based on 100 parts by weight of the polymers.

[0039] Exemplary polymers modified with a monomer that contains an acid anhydride group include acid anhydride-modified ethylene-vinyl acetate copolymers, acid anhydride-modified ethylene-ethyl acrylate copolymers, acid anhydride-modified ethylene-propylene rubbers, acid anhydride-modified low density polyethylenes, acid anhydride-modified linear low density polyethylenes, acid anhydride-modified poly(propylene-ethylene/propylene) copolymers, acid anhydride-modified styrene-butadiene rubbers, acid anhydride-modified hydrogenated styrene-butadiene rubbers, acid anhydride-modified styrene-ethylene/butadiene rubbers, acid anhydride-modified hydrogenated styrene-ethylene/butadiene rubbers, and the like.

[0040] The resin composition can be applied to an electrical conductor to form an insulating covering by any known or later developed method. In particular, the resin composition can be applied to a conductor by extrusion. Preferably, the conductor is covered with the composition to a thickness of from about 0.15 mm to about 0.35 mm, more preferably from about 0.2 mm to about 0.3 mm. If the coating thickness is less than about 0.2 mm, the covered wire may have reduced wear resistance, but may be satisfactory for some purposes. If the coating thickness is more than about 0.3 mm, the covered wire may have reduced flexibility, but may be satisfactory for some purposes.

EXAMPLES

[0041] This invention is illustrated by the following examples, which are merely for the purpose of illustration and are not to be regarded as limiting the scope of the invention, or the manner in which it may be practiced.

[0042] In each of the Examples and Comparative Examples below, the components were continuously mixed and kneaded as follows. The two resin components and the metal hydroxide were fed simultaneously into the input hopper of a twin-shaft extruder having an electrical heating jacket. This extruder was employed to knead the components together. The extruder temperature (inner surface) was 200° C. at entry, rising to 250° C. at exit. At the exit end there was an extrusion head for forming strands from the mixed composition. The extrusion head was maintained at a temperature of 260° C. The resulting strands were passed through a water bath to a pelletizer, to form pellets. The pellets were used to make wire covering, as described below.

Example 1

[0043] 80 parts by weight of a block polymer PP which is a propylene-ethylene block copolymer having more than 50 wt. % propylene (POLYPRO RB610A manufactured by Tokuyama Corporation; melt flow rate (MFR) at 230° C. with a load of 2.16 kg=0.5 g/10 min.), 20 parts by weight of MAH-SEBS (TUFTEC M1913 manufactured by Asahi Kasei Corporation; a styrene-based elastomer obtained by hydrogenating the double bonds of a styrene-butadiene block copolymer to saturation and modifying the copolymer with maleic anhydride) and 90 parts by weight of magnesium hydroxide (untreated) were kneaded with a twin-screw extruder at 250° C. A micrograph of the composition obtained is shown in FIG. 1.

[0044] The resin composition of Example 1 was photographed with a transmission electron microscope (TEM) (model H-800 manufactured by HITACHI). The photograph was taken at an acceleration voltage of 100 KV. First, the sample was cut to a thickness of about 10 μm by a microtome for an electron microscope, and the cut sample was dyed with ruthenic acid (2% aqueous solution) for 2 hours. Then, the dyed sample was mounted in an epoxy resin, and the TEM was employed using an ultra thin intercept method.

[0045] In FIG. 1, the approximately hexagonal particles that are situated at the central part of the picture and the surrounding narrow long particles are the particles of magnesium hydroxide, the dense portion at the periphery of the respective particles is the first polymer (hydrogenated styrene-butadiene elastomer modified with an acid anhydride) which coats the particles, and the space between the particles is the continuous phase of the second polymer (polypropylene).

[0046] As can be seen in FIG. 1, the filler particles hardly coagulate, and are finely dispersed in the continuous phase of the second polymer.

[0047] The resin composition of this Example provides very satisfactory results when used as a covering for an electrical wire.

Comparative Example 1

[0048] A composition was prepared in the manner described in Example 1, except that an unmodified styrene-based elastomer was used, which was obtained by hydrogenating the double bonds of SEBS (TUFTEC H1041 manufactured by Asahi Kasei Corporation; a styrene-butadiene block copolymer) to saturation, in place of MAH-SEBS. The structure of the composition is shown in the micrograph of FIG. 2.

[0049] Comparison of FIGS. 1 and 2 shows that the styrene-based polymer modified by unsaturated carboxylic acid, by reason of its affinity for the magnesium hydroxide filler particles, forms a structure in the mixture in which styrene-based polymer surrounds the filler particles preferentially. This arrangement is advantageous for obtaining properties that are desirable in compositions used in wire covering.

Examples 2 to 41 and Comparative Examples 2 to 5

[0050] The components shown in Tables 1 to 8 were mixed at the amounts shown, and kneaded by a twin-screw extruder at 250° C.

[0051] The resin compositions were obtained by extrusion-molding to a coating thickness of 0.28 mm around a twisted wire conductor having 0.5 mm² cross-section (composed of 7 copper soft wires having a diameter of 0.32 mm). Die nipples having diameters of 1.40 mm and 0.88 mm were used for extrusion molding. The extrusion temperature was 210° C. to 230° C. for the die and 200° C. to 240° C. for the cylinder, and the extrusion molding was carried out at a linear velocity of 50 m/min.

[0052] The flame resistance, tensile strength/elongation, and wear resistance of the coated electric wires obtained in Examples 2 to 41 and Comparative Examples 2 to 5 were measured in accordance with JASO (Japan Automobile Standards Organization) D 611-94. The test methods are described below.

[0053] To test the flame resistance, a test piece was made by cutting the coated electric wire to a length of 300 mm. Then, the test piece was put into a test box made of iron, and horizontally supported. Using a Bunsen burner having a caliber of 10 mm, the edge of the flame was applied to the lower side of the central portion of the test piece for 30 seconds so that it began to combust, and the time of residual flaming after removal of the flame was measured. When the time of residual flame was 15 seconds or less, the sample was regarded as passing, and when the time of residual flame exceeded 15 seconds, the sample was regarded as failing.

[0054] The wear resistance was measured by a blade reciprocating method. A test piece was made by cutting the coated electric wire to a length of 750 mm. A blade was reciprocated over a length of 10 mm in the axial direction on the surface of the coating material of the test piece. The test piece was fixed on a stand at room temperature (25° C.), and the coating material was worn. The number of reciprocating cycles until the blade reached the conductor was measured when the blade was reciprocated at a load of 7N and a speed of 50 cycles per minute.

[0055] Then, the test piece was moved by 100 mm, rotated by 90 degrees in a clockwise direction, and the above-described procedure was repeated. The procedure was repeated three times for each test piece, and those for which the minimum value was 150 cycles or more were regarded as passing.

[0056] A test piece (a tubular article of only the wire covering) was made by cutting the coated electric wire to a length of 150 mm and removing its conductor. Then, mark lines were aligned to a central portion. Then, with both ends of the test piece installed in the chucks of a tensile tester at room temperature (23±5° C.), the test piece was stretched at a tensile speed of 200 mm/min., and the load at breaking of the test piece and the distance between the mark lines at break were measured. A sample having a tensile strength of 15.7 MPa or more and an elongation of 125% or more was regarded as passing.

[0057] Flexibility was evaluated by touch when the electric wire was bent.

[0058] Processability was evaluated by the presence or absence of whisker formation when the end of the electric wire was peeled. Those having no whiskers were regarded as passing.

[0059] The results are shown in Tables 1 to 8. The amounts of components in the Tables are in units of “parts by weight.” TABLE 1 E2 E3 E4 E5 E6 CE2 Block copolymer PP¹ 60 97 80 90 80 100 MAH-EVA² 40 3 20 10 20 — Magnesium hydroxide A³ 70 90 — — 90 80 Magnesium hydroxide B⁴ — — 30 200 — — Antioxidant⁵ 1 1 1 1 1 1 Total 171 191 131 301 191 181 Tensile elongation (%) >500 >500 >500 180 >500 >500 Tensile strength (MPa) 26 34 36 21 35 34 Flame-retardance Pass Pass Pass Pass Pass Pass Wear resistance (cycle) 300 1200 750 200 600 3000 Flexibility Good Good Good Good Good Bad Processability Pass Pass Pass Pass Pass Reject

[0060] TABLE 2 E7 E8 E9 E10 E11 CE2 Block copolymer PP¹ 60 97 80 90 80 100 MAH-EEA⁶ 40 3 20 10 20 — Magnesium hydroxide A³ 70 90 — — 90 80 Magnesium hydroxide B⁴ — — 30 200 — — Antioxidant⁵ 1 1 1 1 1 1 Total 171 191 131 301 191 181 Tensile elongation (%) >500 >500 >500 180 >500 >500 Tensile strength (MPa) 23 27 30 19 32 34 Flame-retardance Pass Pass Pass Pass Pass Pass Wear resistance (cycle) 280 1100 650 200 500 500 Flexibility Good Good Good Good Good Bad Processability Pass Pass Pass Pass Pass Reject

[0061] TABLE 3 E12 E13 E14 E15 E16 CE3 Block copolymer PP¹ 60 97 80 90 80 80 MAH-EPR⁷ 40 3 20 10 20 — EPR⁸ — — — — — 20 Magnesium hydroxide A³ 70 90 — — 90 90 Magnesium hydroxide B⁴ — — 30 200 — — Antioxidant⁵ 1 1 1 1 1 1 Total 171 191 131 301 191 191 Tensile elongation (%) >500 >500 >500 160 >500 >500 Tensile strength (MPa) 24 27 25 19 28 2 Flame-retardance Pass Pass Pass Pass Pass Pass Wear resistance (cycle) 220 900 700 200 400. 70 Flexibility Good Good Good Good Good Bad Processability Pass Pass Pass Pass Pass Reject

[0062] TABLE 4 E17 E18 E19 E20 E21 CE2 Block copolymer PP¹ 60 97 80 90 80 100 MAH-LDPE⁹ 40 3 20 10 20 — Magnesium hydroxide A³ 70 90 — — 90 80 Magnesium hydroxide B⁴ — — 30 200 — — Antioxidant⁵ 1 1 1 1 1 1 Total 171 191 131 301 191 181 Tensile elongation (%) >500 >500 >500 180 >500 >500 Tensile strength (MPa) 25 30 31 18 25 34 Flame-retardance Pass Pass Pass Pass Pass Pass Wear resistance (cycle) 200 1250 700 250 600 3000 Flexibility Good Good Good Good Good Bad Processability Pass Pass Pass Pass Pass Reject

[0063] TABLE 5 E22 E23 E24 E25 E26 CE2 Block copolymer PP¹ 60 97 80 90 80 100 MAH-LLDPE¹⁰ 40 3 20 10 20 — Magnesium hydroxide A³ 70 90 — — 90 80 Magnesium hydroxide B⁴ — — 30 200 — — Antioxidant⁵ 1 1 1 1 1 1 Total 171 191 131 301 191 181 Tensile elongation (%) >500 >500 >500 60 >500 >500 Tensile strength (MPa) 27 32 33 20 26 34 Flame-retardance Pass Pass Pass Pass Pass Pass Wear resistance (cycle) 240 1300 750 300 700 3000 Flexibility Good Good Good Good Good Bad Processability Pass Pass Pass Pass Pass Reject

[0064] TABLE 6 E27 E28 E29 E30 E31 CE2 Block copolymer PP¹ 60 97 80 90 80 100 MAH-PP/EPR¹¹ 40 3 20 10 20 — Magnesium hydroxide A³ 70 90 — — 90 80 Magnesium hydroxide B⁴ — — 30 200 — Antioxidant⁵ 1 1 1 1 1 1 Total 171 191 131 301 191 181 Tensile elongation (%) >500 >500 >500 200 >500 >500 Tensile strength (MPa) 23 27 26 25 30 34 Flame-retardance Pass Pass Pass Pass Pass Pass Wear resistance (cycle) 200 1200 1800 210 1800 3000 Flexibility Good Good Good Good Good Bad Processability Pass Pass Pass Pass Pass Reject

[0065] TABLE 7 E32 E33 E34 E35 E36 CE4 Block copolymer PP¹ 60 97 80 90 80 80 MAH-HSBR¹² 40 3 20 10 20 — HSBR¹³ — — — — — 20 Magnesium hydroxide A³ 70 90 — — 90 80 Magnesium hydroxide B⁴ — — 30 200 — — Antioxidant⁵ 1 1 1 1 1 1 Total 171 191 131 301 191 191 Tensile elongation (%) >300 >500 >500 170 >500 >500 Tensile strength (MPa) 27 30 31 24 30 34 Flame-retardance Pass Pass Pass Pass Pass Pass Wear resistance (cycle) 400 1500 2500 260 1800 110 Flexibility Good Good Good Good Good Bad Processability Pass Pass Pass Pass Pass Reject

[0066] TABLE 8 E37 E38 E39 E40 E41 CE5 Block copolymer PP¹ 60 97 80 90 80 80 MAH-SEPS¹⁴ 40 3 20 10 20 — SBPS¹⁵ — — — — — 20 Magnesium hydroxide A³ 70 90 — — 90 80 Magnesium hydroxide B⁴ — — 30 200 — — Antioxidant⁵ 1 1 1 1 1 1 Total 171 191 131 301 191 191 Tensile elongation (%) 250 >500 >500 170 >500 700 Tensile strength (MPa) 25 28 26 27 28 27 Flame-retardance Pass Pass Pass Pass Pass Pass Wear resistance (cycle) 400 1300 1200 260 1700 90 Flexibility Good Good Good Good Good Good Processability Pass Pass Pass Pass Pass Pass

Examples 42 to 51

[0067] In Examples 42 to 46 of this invention, the following components were kneaded at the ratios shown in Table 9 to prepare resin compositions

[0068] Using an extrusion molding machine, each composition was applied at a thickness of 0.28 mm to a conductor (seven soft copper wires twisted together and circularly compressed to give a smooth peripheral surface) having a cross-sectional area of 0.5 mm² to prepare an electrical wire. The die nipples used in the extrusion molding had diameters of 1.40 mm and 0.88 mm. The extrusion temperature of the die was 210° C. to 230° C. The extrusion temperature of the cylinder was 200° C. to 240° C. The linear speed was 50 m/minute.

[0069] In Examples 47 to 51 of the invention, the same components as used in Examples 42 to 46 were kneaded at the ratios shown in Table 3 to prepare compositions selected to be suitable for use in an electrical wire having a small diameter. Using an extrusion molding machine, the composition was applied at a thickness of 0.20 mm to a conductor (seven soft copper wires twisted together and circularly compressed to give a smooth peripheral surface) having a cross-sectional area of 0.13 mm² to prepare the covered wire. The die nipples used in the extrusion molding had diameters of 0.50 mm and 0.90 mm. The extrusion temperature of the die was 210° C. to 230° C. The extrusion temperature of the cylinder was 200° C. to 240° C. The linear speed was 50 m/minute.

[0070] The covered electrical wires of the examples were tested to examine flame resistance (fire resistance), wear resistance, tensile strength, tensile elongation, flexibility, and processability, as described below.

[0071] A flame resistance test was conducted in accordance with JASO D611-94 of Japanese Automobile Standards Organization, as described above.

[0072] In accordance with JASO D611-94, a wear resistance test was conducted as described above. In the case of Examples 42 to 46, specimens for which the blade reciprocated more than 150 times were regarded as successful. In the case of Examples 47 to 51, specimens for which the blade reciprocated more than 100 times were regarded as successful.

[0073] In accordance with JASO D611-94, tensile strength and tensile elongation tests were conducted as described above.

[0074] Flexibility was evaluated by touch. Specimens which gave a good feeling when they were bent by hand were regarded as successful.

[0075] To test processability, part of the resin composition disposed at the end of each covered wire was peeled off from the conductor to check whether a whisker was formed. Specimens on which no whisker was formed were regarded as successful.

[0076] Tables 9 and 10 show the components (in parts by weight) of each resin composition and the results obtained for each electrical wire. TABLE 9 E42 E43 E44 E45 E46 Block copolymer PP¹ 60 97 80 90 80 MAH-SEBS¹⁶ 40 3 20 10 20 Magnesium hydroxide A³ 70 90 — — 90 Magnesium hydroxide B⁴ — — 50 200 — Antioxidant⁵ 1 1 1 1 1 Total (parts by weight) 171 191 151 301 191 Fire resistance Pass Pass Pass Pass Pass Wear resistance (reciprocation 500 1800 4000 300 2000 number of blade) Tensile strength (MPa) 28 31 34 23 33 Tensile elongation (%) 200 420 520 160 320 Flexibility Good Good Good Good Good Processability Pass Pass Pass Pass Pass

[0077] TABLE 10 E47 E48 E49 E50 E51 Block copolymer PP¹ 95 90 80 65 80 MAH-SEBS¹⁶ 5 10 20 35 20 Magnesium hydroxide B⁴ 120 150 200 160 100 Antioxidant⁵ 1 1 1 1 1 Total (parts by weight) 221 251 301 261 201 Fire resistance Pass Pass Pass Pass Pass Wear resistance (reciprocation Over Over Over 180 Over number of blade) 500 500 500 500 Tensile strength (MPa) 32 30 32 30 29 Tensile elongation (%) 260 220 210 250 265 Flexibility Good Good Good Good Good Processability Pass Pass Pass Pass Pass

[0078] The coated wires of each of Examples 42 to 51 of this invention were satisfactory in fire resistance, wear resistance, tensile strength, tensile elongation, flexibility and processability. In particular, the resin compositions of each of Examples 44 and 46, shown in Table 9, had desirable mechanical strength properties, such as wear resistance, tensile strength and tensile elongation, and a good balance between these characteristics. Each of these compositions contained 70 to 90 parts by weight of the propylene resin and 10 to 30 parts by weight of the styrene thermoplastic elastomer modified with the unsaturated carboxylic acid or its derivative and 50 to 150 parts by weight of the metal hydroxide per 100 parts by weight of the polymers.

[0079] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention. 

What is claimed is:
 1. An electrical wire, comprising: a conductor; and an electrically insulating covering formed on the conductor; wherein: the covering is a resin composition comprising at least one first polymer, at least one second polymer and filler particles; the at least one first polymer has a higher bonding affinity to the filler particles than the at least one second polymer; and the filler particles are coated with the at least one first polymer and the coated filler particles are embedded in a matrix of the at least one second polymer.
 2. The electrical wire of claim 1, wherein the filler particles are inorganic filler particles.
 3. The electrical wire of claim 2, wherein the inorganic filler particles are comprised of at least one filler material selected from the group consisting of carbon materials, metal oxides, metal hydroxides, metal carbonates, metal sulfates, metal silicates and metal nitrides.
 4. The electrical wire of claim 3, wherein the inorganic filler particles are comprised of at least one metal hydroxide.
 5. The electrical wire of claim 1, wherein the filler particles are surface coated with a coupling agent.
 6. The electrical wire of claim 5, wherein the coupling agent is selected from the group consisting of silane coupling agents, fatty acids and salts of fatty acids.
 7. The electrical wire of claim 1, wherein the at least one first polymer comprises a reactive functional group that promotes bonding of the at least one first polymer with the filler particles.
 8. The electrical wire of claim 7, wherein the reactive functional group is selected from the group consisting of carboxylic acid groups, carboxylic acid anhydride groups and carboxylic acid ester groups.
 9. The electrical wire of claim 8, wherein the at least one first polymer is selected from the group consisting of acid anhydride-modified ethylene-vinyl acetate copolymers, acid anhydride-modified ethylene-ethyl acrylate copolymers, acid anhydride-modified ethylene-propylene rubbers, acid anhydride-modified low density polyethylenes, acid anhydride-modified linear low density polyethylenes, acid anhydride-modified poly(propylene-ethylene/propylene) copolymers, acid anhydride-modified styrene-butadiene rubbers, and acid anhydride-modified hydrogenated styrene-butadiene rubbers.
 10. The electrical wire of claim 1, wherein the at least one second polymer is selected from the group consisting of propylene polymers, ethylene polymers, and ethylene/propylene copolymers.
 11. A method of making an electrical wire, comprising: forming a resin composition comprising at least one first polymer, at least one second polymer and filler particles, the at least one first polymer having a higher bonding affinity to the filler particles than the at least one second polymer, the filler particles being coated with the at least one first polymer, and the coated filler particles being embedded in a matrix of the at least one second polymer; and applying the resin composition to an electrical conductor to form an electrically insulating covering on the electrical conductor; wherein forming the resin composition comprises one of: (i) first kneading the filler particles and the at least one first polymer to form a mixture and subsequently kneading the mixture and the at least one second polymer; and (ii) kneading the filler particles, the at least one first polymer and the at least one second polymer together simultaneously.
 12. The method of claim 11, wherein forming the resin composition comprises first kneading the filler particles and the at least one first polymer to form a mixture, and subsequently kneading the mixture and the at least one second polymer.
 13. The method of claim 11, wherein forming the resin composition comprises kneading the filler particles, the at least one first polymer and the at least one second polymer together simultaneously.
 14. The method of claim 11, wherein the filler particles are comprised of an inorganic filler.
 15. The method of claim 14, wherein the inorganic filler is selected from the group consisting of carbon materials, metal oxides, metal hydroxides, metal carbonates, metal sulfates, metal silicates and metal nitrides.
 16. The method of claim 15, wherein the inorganic filler is comprised of at least one metal hydroxide.
 17. The method of claim 11, wherein the filler particles are surface treated with a coupling agent.
 18. The method of claim 17, wherein the coupling agent is selected from the group consisting of silane coupling agents, fatty acids and salts of fatty acids.
 19. The method of claim 11, wherein the at least one first polymer comprises a reactive functional group that promotes bonding of the at least one first polymer with the filler particles.
 20. The method of claim 19, wherein the reactive functional group is selected from the group consisting of carboxylic acid groups, carboxylic acid anhydride groups and carboxylic acid ester groups.
 21. The method of claim 20, wherein the at least one first polymer is selected from the group consisting of acid anhydride-modified ethylene-vinyl acetate copolymers, acid anhydride-modified ethylene-ethyl acrylate copolymers, acid anhydride-modified ethylene-propylene rubbers, acid anhydride-modified low density polyethylenes, acid anhydride-modified linear low density polyethylenes, acid anhydride-modified poly(propylene-ethylene/propylene) copolymers, acid anhydride-modified styrene-butadiene rubbers, and acid anhydride-modified hydrogenated styrene-butadiene rubbers.
 22. The method of claim 11, wherein said second polymer is selected from the group consisting of propylene polymers, ethylene polymers, and ethylene/propylene copolymers. 